The use of electrical connectors in the environment of an aircraft requires consideration of a number of conditions which might not otherwise require critical attention. For example, air pressure decreases from 14.7 psi at sea level to one millionth of a kilogram at an altitude of 70 miles. Temperature, humidity, solar radiation, wind, rain, temperature, shock, zero gravity, and ozone levels are just a few of the factors which must be considered when designing electrical connectors for an avionic environment. Among the most critical of such conditions are the affect of mechanical stress, vibration, electromagnetic interference (EMI) and radio frequency interference (RFI).
The walls of commercial aircraft pressurized cabins are cold relative to the heated environmental system employed to make passengers comfortable at high altitudes. Moisture forms where the walls interface the heated cabin. This moisture can run underneath the floors and condense on the electrical connector terminals located within the aircraft skin structure. The condensed moisture may cause corrosion. Cables running within the skin structure must be reliably designed since the condition of the electrical connector terminals which connect the cables are difficult to monitor.
In the conventional art, rectangular connectors have been used to mate a matrix pattern of electrical pin contacts with a matrix pattern of electrical contact sockets. Chamfered mating edges insure easy polarized alignment of rectangularly shaped electrical connectors. However, rectangular connectors rely primarily on friction coupling to support the electrical contact. This method of coupling may only be used where the connector halves will not be subjected to any vibrations or movement, or where they will be under no undue strain or pressure. Therefore, in the aircraft environment, subject to considerable moisture and vibration, rectangular coupling arrangements may not be satisfactory.
Circular connectors are highly desirable for use in the aircraft environments. Standard screw thread couplings have been used which have a coupling nut collaring an electrical plug. The plug coupling nut is then screwed onto an electrical receptacle shell. But, such conventional screw threads require numerous turns to fully mate the plug and receptacle shells, and safety wiring of the coupling nut is required for secure mating. Acme-threaded couplings (of a high or zero pitch variety), as disclosed in U.S. Patent No. RE 31,462 to McCormick (original U.S. Pat. No. 3,848,950) reduce the number of threadings required when compared with the standard thread coupling. However, both the Acme-threaded coupling and the standard screw thread do not provide as quick a decoupling mechanism as is necessary in an aircraft environment.
An attempt to improve upon the Acme-threaded connector coupling is disclosed in U.S. Pat. No. 3,750,087 to Vetter. This patent discloses a detent ball on the receptacle shell which rides the bayonet groove in the coupling nut mechanism of a plug connector. As one turns the coupling nut to lock the connector plug into the receptacle shell, the detent ball advances along a bayonet groove until it locks in a detent. A wave spring washer maintains pressure to assure ball/detent lock. This method of coupling, although representing an improvement, provides a preloaded stress to the spring washer which it may not be able to withstand under all conditions.
U.S. Pat. No. 4,056,298 to Cooper discloses a flanged retainer ring which is in abutment within the walls of a coupling ring housing in such a manner that the ring is rotated 90 degrees along the circumference of the inner diameter of the coupling ring housing and then translated axially forward to lock as a breach lock, into a fixed position when the connector is fully mated. FIGS. 22 through 25 of this Cooper patent clearly illustrate this breach lock feature. This coupling arrangement requires only a partial rotation of the coupling nut to lock the electrical connector assembly into a fully mated condition. However, this coupling is dependent upon the strength of helical spring 91 pressing the retainer ring 92 forward in abutment with the inner diameter of the coupling ring housing 71. In a severe mechanical vibrational environment, such as is common in aircraft, this breach lock arrangement may uncouple.
An attempt to supplement this design is suggested in U.S. Pat. No. 4,277,125 to Ball. In this patent, there is disclosed an arcuate detent member, U-shaped in design, having extended convex surfaces forming a pair of dog legs for insertion radially within a detent recess. With reference to FIG. 7 of the Ball patent, as one rotates the coupling nut, through 90 degrees, the detent member causes the connector to latch at a fully open and fully mated position. Like the breach lock of the Cooper patent, this Ball patent has a breach lock mechanism for securing the coupling of the electrical connector plug to the receptacle shell. This arcuate detent, wishbone in shape, under extreme mechanical vibration may break or fracture, giving rise to a "wounded" dog leg which could obstruct the detent groove and prevent rotation of the coupling nut.
Although circular connectors provide a stronger and more vibration-resistant coupling than rectangular connectors, they require some form of polarization, so that as the coupling draws the electrical connector plug into the connector receptacle, the matrix pattern of pins and sockets will be in proper alignment.
The conventional art of the Vetter patent also discloses a mechanism having fixed bayonet pins protruding radially outwardly from the collar of a receptacle shell. The connector shell is telescoped within the receptacle shell, while a coupling ring is rotated which surrounds the connector shell in order to advance the connector shell forward into a fully mated position. As the coupling ring is turned, the fixed bayonet pins ride a helical bayonet groove scored along the inner diameter of the coupling ring. The terminals of the bayonet grooves are orifices which accommodate the securement of the bayonet pins of the receptacle into the coupling ring. This locking mechanism represents an improvement over other forms of connector coupling systems, but the fixed bayonet design may not have sufficient flexibility for reliable coupling under conditions of mechanical stress or vibration. For example, if the fixed bayonet pin becomes bent, it may no longer ride the bayonet groove properly and thereby prevent necessary coupling or decoupling of electrical connections within an aircraft.
What is needed is a coupling mechanism which provides the advantages of the previously described bayonet groove coupling in a more reliable manner.
Furthermore, when an electrical connector plug is attached to the free end of a cable, for quick coupling and decoupling with a fixed or mounted circular receptacle shell, it is important that the polarization system, within the plug, for directing the alignment of the plug and receptacle is preserved. Heretofore, no design previously known to the inventors has been directed to solving the problem of the inadvertent misalignment of the electical connector plug assembly, when that assembly is not fully mated to an electrical connector receptacle shell. As noted earlier, the receptacle shell may have a polarization key or keyway for accommodating a properly aligned electrical connector plug for mating. Since a coupling ring or nut provides quick and useful leverage for securing the mechanical coupling of connector receptacles and plugs, it is necessary to make certain that the initial position of the coupling ring and the connector shell of the electrical connector plugs are in proper alignment before an attempt is made to mate this assembly with an electrical receptacle shell. Heretofore, aircraft mechanics, unfamiliar with the detailed operation of complex electrical plug assemblies, have inadvertently (usually through release of the compression retainer ring apparatus housed at the rear of an electrical connector plug assembly) placed the coupling ring or nut out of alignment with the connector shell. When this technician later attempted to mate a misaligned electrical plug with an electrical receptacle shell, he found that he was unable to do so. What is needed is a mechanism housed within the electrical connector plug assembly which would prevent the inadvertent misalignment of the coupling ring or housing with the connector shell of the electrical connector plug. Such a mechanism could lock the polarization and alignment of the electrical connector plug assembly except when the plug has been placed in position for fully mating with the electrical connector receptacle.
The invention disclosed herein is an improved design which presents, in combination, an improved bayonet grooved coupling mechanism with a mechanism for preventing misalignment of components within the electrical plug assembly prior to mating with a receptacle shell.